The present invention relates to the field of medical devices and more particularly to guidewires for vascular procedures.
Medical guidewires for vascular procedures, such as angioplasty procedures, diagnostic and interventional procedures, percutaneous access procedures, or radiological and neuroradiological procedures in general, traditionally comprise an elongated core element with one or more tapered sections near the distal end thereof and a flexible helical coil disposed about the distal portion of the core element. The distal extremity of the core element or a separate safety ribbon which is secured to the distal extremity of the core element extends through the flexible coil and is secured to the distal end member of the guidewire, which is a rounded member at the distal end of the helical coil. Torquing means are provided on the proximal end of the core element to rotate and steer the guidewire while it is being advanced through a patient""s vascular system.
The physician views the progress on a screen and makes the distal end of the guidewire enter and follow tortuous vascular vessels from the entry site through the various vascular branches to the target site by pushing and rotating the proximal end of the guidewire outside of the patient. In connection with the advancement of the guidewire or once the guidewire has been positioned at the desired site, a wide variety of medical devices may be directed to the target site along the guidewire by simply sliding the device over the guidewire and advance the device to the distal end of the guidewire. A typical medical device is a catheter, and very often a catheter and the guidewire are introduced in a common procedure where the guidewire is advanced a distance in front of the catheter, then the catheter is advanced over the guidewire, followed by a further advancement of the guidewire. Following placement of the catheter or other device, the guide wire can be removed if desired.
The flexible coil acts as a protective measure of a suitably large diameter, hindering the guidewire core in damaging the vascular wall. The above mentioned guidewire is known from U.S. Pat. No. 4,619,274 to Morrison whose guidewire has a progressively attenuated diameter. An elongated core element extends from the proximal to the distal ends of the guidewire and has a decreasing cross sectional area in a direction towards the distal end member. A coil is carried by and secured to said core element and has proximal and distal ends. The coil has a diameter which decreases in a direction towards the distal end. The coil is formed of a single helical wound wire which has a diameter which decreases from one end to the other end with the larger diameter beginning in a region closer to the proximal end and the smaller diameter wire ending in a region closer to the distal end.
U.S. Pat. No. 5,001,825 to Halpern describes a fabrication process for a guidewire core where a solid metal wire is drawn down in several stages to have a stepwise decreasing diameter towards the distal end. The core is surrounded by a flexible coil having an outer diameter which decreases near the distal end. The coil consists of a single helical wound wire having a constant cross sectional area.
It is an object of the present invention to provide a guidewire which in its distal area is highly flexible and yet capable of transferring torques applied to the proximal end of the guidewire to the distal end of the guidewire in a very precise manner even when the guidewire follows a loop-shaped course.
The present invention relates to a guidewire comprising a distal end member and a shaft portion extending in a longitudinal direction from a proximal end towards the distal end member, and at least one helical wound wire extending from a position at the shaft portion to the distal end member. In view of this, the guidewire according to the present invention is characterized in that at least one helical wound group of at least two wires extending side by side has a pitch angle in the range of 35xc2x0-76xc2x0.
In the prior art guidewires the core element transfers the torque to the distal area of the guidewire, but the core element also restricts the flexibility of the guidewire. When the core element is given a very small diameter in its distal area in order to improve the flexibility, it loses the ability to transfer the torque. When, according to the invention, the flexible coil in the distal end of the guidewire is made of two or more wires which are wound with a pitch angle in the specified range, the wound wires transfer torque and also force components directed in the axial direction of the guidewire to the distal end thereof.
The guidewire surprisingly maintains its capabilities for transferring torque when it follows a tortuous path involving two or more loops. The torque is transferred all the way to the distal end member or tip of the guidewire, meaning that the distal end member can be very precisely steered from the proximal end. If the pitch angle exceeds 80xc2x0 the ability to transfer torque is lost.
In a preferred embodiment, along a distance of at least 10 cm from the distal end member said at least one helical wound group of wires is the primary or the sole torque-transferring means between the shaft portion and the distal end member. Because the torque is transferred through the helical wound wires the central core can be given very feeble dimensions, thus increasing the flexibility of the distal portion, or it can be completely left out by making at least the most distal 10 cm of the guidewire without a torque-transferring solid metallic core inside said at least one group of wires. If desired there can be a safety ribbon inside the wound wires, connecting the rounded distal end member with a more proximal shaft portion, but such a ribbon will normally not be required.
Due to the very high flexibility, pushability and torquability and the ability of the guidewire to maintain each of these three characteristics even when set in a very tortuous pattern involving two or more tight loops the guidewire can be of use in very small and distant vessels. In order to further enhance use of the guidewire in vessels with small lumen the at least one helical wound group of wires has a smaller outer diameter at the distal end than at said position on the shaft portion.
If the group of wound wires is secured to the shaft, which for example can be of traditional type with a core member or can be another group of wires of larger dimensions, such as by soldering or welding the proximal end of the group onto the shaft the guidewire can be prone to kinking at the transition between the flexible group of wires and the remainder of the shaft. With a view to avoiding this, the said at least one helical wound group of wires preferably extends into the shaft portion towards the proximal end, and even more preferably it extends along a guidewire length at least in the range of 20-50 cm from the distal end. The additional stiffness caused by the attachment of the wire is less disturbing the longer it occurs from the distal end of the guidewire. It is possible to let the group or groups of helical wound wires extend to a position at the proximal end of the guidewire, so that they span the entire guidewire. It is preferred that the wires in said at least one group have a separation from one wire to the next in the group of less than the diameter of the wire. Normally, the wires in the group are placed so close they touch each other.
In one embodiment the at least one of the wires in said at least one group is ribbon-shaped. The widest cross sectional dimension, the breadth of the wire is directed in the longitudinal direction of the guide-wire. It is preferred that the ribbon-shaped wire has rounded edges.
In a preferred embodiment the at least one group of wires is made of from 2 to 8 helical wound wires. A number of the wires are placed next to each other and winded in the same direction. By using several wires their aggregate breadth can be adapted to correspond to the desired pitch distance. As an alternative to winding all wires in the same direction some, such as one half of the number of wires, can be winded in one direction while others, such as the other half, can be winded in the opposite direction. Such winding can be effected in separate rounds resulting in a coil of two layers of wires with mutual opposite handedness.
In the preferred embodiment the guidewire is made without a solid or hollow metallic core inside the at least one coil. By dispensing with the metallic core the flexibility of the guidewire is increased, and the manufacturing of the guidewire is simplified.
In an embodiment the cross-section of said wires in said at least one helical wound group is a circular shape in the proximal end of the wire, and in the distal portion of the wire the cross-section has the shape of a circular segment which has a straight line facing radially outwards. Such a variation of the cross-sectional shape can be the result of grinding of a helical wound wire on its outside with the purpose of reducing the diameter of the helical wound wire in its distal portion. The circular segment has less cross sectional area than the corresponding full circular, shape, and the reduced cross-sectional area greatly increases the bending flexibility of the helical wound wire without sacrificing its ability to transfer torque.
In another aspect the present invention relates to a guidewire comprising a distal end, a shaft portion and a proximal end, wherein the shaft portion comprises at least one helical wound group of at least two wires having a pitch angle in the range of 35xc2x0-72xc2x0, and said at least one helical wound group of wires having said pitch angle extends to the distal end of the guidewire. With this guidewire the above mentioned advantages are achieved.
The present invention further relates to a method of manufacturing a guidewire, wherein a guidewire body is provided, said body comprising at least one helical wound group of at least two wires having a pitch angle in the range of 35xc2x0-76xc2x0, wherein an elongate distal guidewire portion of said at least one helical wound wire is subjected to grinding reducing the outer diameter of said distal guidewire portion in relation to a proximal portion of the guide wire. Grinding is an advantageous manner of manufacturing the above mentioned guidewires because it is very easy to adapt the grinding process to the specific guidewire to be produced, and a wide variety of guidewires can be premanufactured as wound guidewire bodies having an even outer diameter along their entire length. When the specific use of the guidewire is specified, such as a guidewire for accessing a kidney in an adult via the femoral route, which requires a guidewire having a relatively long portion with the full diameter and a relatively short portion with a quickly reduced diameter, or a guidewire for neuroradiological use via the femoral route, which requires a gentle reduction in diameter over a relatively long distance and a long and soft distal portion, it is a simple matter to adjust the grinding process to the desired guidewire.
The method can be adjusted to grind the elongate distal portion of the guide wire to have a substantially continuously diminishing outer diameter which results in a gradual increase of bending flexibility of the guidewire.
It is further possible to adjust the method to grind the elongate distal portion of the guide wire to have a substantially stepwise diminishing outer diameter which is often preferable in case of very long distal portions. Further, the method can be so that elongate distal portions of the guide wire are ground to have areas with diminishing outer diameters mixed with areas having substantially constant outer diameters.